1. Field of Invention
The present invention relates to a field of manufacturing a superhard-material tool, and more particularly to a high-performance metal matrix diamond composite material used for cutting a semiconductor QFN (Quad Flat No-Lead) packaging device and a method for preparing a high-precision thin saw blade product thereof.
2. Description of Related Arts
QFN package is one of the main techniques in semiconductor high-ranking package testing fields currently. As integrated circuit (IC) components are developing towards directions of super integration, reducing overall dimension, enhancing heat dissipation performance, and improving electrical property, the QFN package has obvious advantages.
QFN package substrate is formed by injection molding copper lead frame and resin polymers. At least one chip grain is distributed in stack or spreaded smoothly and corresponding leaders connected with each other thereof is wrapped and sealed in the QFN package substrate. An overall thickness of the QFN package substrate is within a range of 0.8-1.0 mm, wherein the copper lead frame has a thickness of 0.2 mm, and usually has tin alloy or nickel alloy with a thickness of 0.02 mm plated thereon; the polymers has a thickness of 0.6-0.8 mm, and consists of epoxy resin and inorganic filler filled in the epoxy resin, such as grains of Si2O3 or Al2O3.
After IC chip grains is processed by QFN packaging, each chip having an individual function must be processed by dividing in monomer for being applicable in a terminal equipment, which is an important and unavoidable working procedure in semi-conductor industry chains so far.
Saw-type cutting is a dominant method of performing the working procedure, and a saw blade employed thereby is a diamond device similar to a grinding wheel. The saw blade mainly comprises diamond grains and bonding agent matrix, which is usually installed on a special dicing saw and performs linear cutting on packaging substrates by the diamond grains exposed on an cutting edge of the saw blade, in such a manner that a monomer chip having an overall size varying in 3×3-7×7 mm and a cutting quality that meets operating requirements is obtained.
In view of terminal application requirements, basic indexes of cutting quality on production line such as tolerance in shape and size among each single chip, and corresponding defects of broken edges and scratches, are easy to accomplish in commonly working condition. However, the key lies in controlling a longitudinal extension of a copper leader along a direction of thickness, i.e., a burr, and a transverse extension along a direction of cutting, i.e., smearing. Generally requirements in industry are Burr<50 μm, Smearing<⅓-½ pitch. Reasons that changes of the two indexes Burr and Smearing are valued as following. The former influences suitability between each chip and a test connector. If the suitability thereof is bad, normal test is not capable of being implemented smoothly, and the chip is deemed a defective. Further, the latter may lead to a short circuit of interconnection, and destroy use functions ought to be existed in the chip. In addition, overhigh cutting heat generated during cutting process may lead to softening or melting of the copper leader and particularly a coating layer of tin thereon, so that the chip is scrapped, which a phenomenon should be strictly avoided.
As an only choice for cutting QFN packaging devices in industry, a thermosetting resin matrix diamond saw blade has significant advantages which are mainly represented as following. The thermosetting resin matrix diamond saw blade has a well matched wear in a radial direction and a side face, and has a saw blade shape appearance of approximately straight transition, meeting geometrical appearance and dimension requirements of the chip. In addition, the thermosetting resin matrix diamond saw blade has a strong capability of self-sharpening and sharp cutting, which inhibits generation and increase of the bur, the smearing and flanging. Furthermore, the thermosetting resin matrix diamond saw blade is easy to form a cutter exposure and a large debris holding space, which is beneficial to cooling and debris releasing, and is not easy to be blocked. Therefore, a phenomenon of sticking a blade or fusing generated by over heating during grinding and cutting is prevented.
However, from developing requirements of semi-conductor packaging industry, compared with commonly used sintered metal matrix diamond saw blade used for cutting Ball Grind Array (BGA) in industry, drawbacks existed in resin matrix saw blade per se is particularly obvious and mainly presented in following two aspects. Firstly, holding force of the matrix to the diamond is very limited and influenced by an abrasion resistance thereof, diamond grains thereof is easy to fall off untimely, which leads to excessive wear and tear. Thus, cutting length of the resin matrix saw blade is severely insufficient, which is no more than about 1000 meters and even not exceeding 500 m, and thus is not beneficial to reducing production cost thereof. Improving volume percentage concentration of the diamond to not less than 80%, and increasing a size of the diamond grains to 45-75 μm is usually adopted to prolong a service life of the resin matrix saw blade, but little effect is obtained. Secondly, a phenomenon of chipping or embrittlement is easy to emerge, which limits promoting of cutting efficiency. In actual production, feeding speed of elements bore by the resin matrix saw blade is usually set at a rang of 35-45 mm/s. If the feeding speed setting exceeds the rang, cutting quality of the chip reduces, or seriously, wear and tear of the saw blade is speed up or even causes abnormal effectiveness. All phenomenons mentioned above are due to characteristics of component materials of the matrix.
Limited by the characteristics of component materials per se and preparation technology thereof, the resin matrix saw blade is not capable of promoting greatly in improving the cutting efficiency and prolonging service life thereof. Therefore, it is necessary to seek and develop new alternatives, so as to promote updating and upgrading the WQFN saw blade products used for cutting the packaging device.
Compared with the resin matrix saw blade, advantages of the sintered metal matrix saw blade are following. By hot-pressing sintering, the metal matrix thereof approximately reaches a level of alloying. By strengthening function of metallic compound having a complex lattice structure formed thereon, the sintered metal matrix saw blade has mechanical characteristics of large modulus of elasticity, high yield strength, high abrasive resistance and etc, in such a manner that tightness of wrap between the metal matrix and the diamond grains is enhanced, and holding mechanism by force therebetween is formed. A combining position between the metal matrix and the diamond has no apparent crack, and a surface of the diamond falling off hole is approximately flat and smooth. This holding mechanism of combining not only firmly holds the diamond grains, but prompts the sintered metal matrix saw blade to form a high cutter exposure to ensure cutting sharpness of the saw blade, and is easy to form a large debris capacity groove, which effectively prevents blocking by the debris and enhances heat-sinking capability thereof in cooling.
Thus, searching on formula constitution system and corresponding preparing method of the sintered metal matrix diamond saw blade is capable of significantly improving processing efficiency or prolonging a service life thereof on the premise of ensuring cutting quality of the chip on production line, and thus is beneficial to reducing manufacturing cost thereof. Based on the very application background, applying for the present invention is of great significance for supporting the development of IC packaging industry.